RSA Keypair Generator

About RSA keypair generator

This generator creates an RSA public and private key and exports them as standard PEM blocks that OpenSSL, most languages and many services can read. You choose whether the key is for encryption (RSA-OAEP) or signing (RSASSA-PKCS1-v1_5), the modulus size, and the hash, and can download each half as a file.

How to use it

1. Under Algorithm, choose RSA-OAEP for encryption and decryption, or RSASSA-PKCS1-v1_5 for signing and verification.
2. Pick a Key size of 2048, 3072 or 4096 bits and a Hash of SHA-256, SHA-384 or SHA-512.
3. Select Generate keypair and wait. A badge then shows how many seconds it took.
4. Copy or Download the public key as public-key.pem and the private key as private-key.pem.

What the export looks like

RSA-OAEP, 2048 bits, SHA-256

A public key in SPKI form beginning -----BEGIN PUBLIC KEY----- followed by MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A, and a private key in PKCS#8 form beginning -----BEGIN PRIVATE KEY-----. The remaining characters are random.

When to use it

• Creating a throwaway keypair for a test environment or a code sample.
• Producing the key for a service that asks you to upload a public key for signature verification.
• Learning how PEM, SPKI and PKCS#8 relate by looking at real exported keys.
• Getting a key with a specific size and hash to test how your library handles it.

Questions about RSA keypair generator

Which key size should I pick?

2048 bits is the common baseline and fastest. 3072 bits matches roughly 128-bit security in NIST's guidance, and 4096 bits is slower to generate, taking seconds and possibly freezing the tab briefly.

Why is the hash chosen at generation time?

Web Crypto binds the hash to the key. It is not stored in the PEM, so when you import the key later you must name the same hash, or OAEP decryption and signature checks will fail.

Is the private key protected with a passphrase?

No. The PKCS#8 PEM is unencrypted, so anyone who gets the file can use the key. The page warns that it exists only while the tab stays open, so save it somewhere secret before leaving.

Which public exponent is used?

The standard value 65537, chosen because it is prime, small enough for fast verification, and avoids the pitfalls of very small exponents such as 3.

Can I use one key for both encryption and signing?

This tool does not create one. Each pair is limited to its own usage, and mixing purposes in a single key is discouraged because a weakness in one use can expose the other.

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